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The RCP 8.5 Cheat

03 Oct 2020 | Fact Checks



John Robson

If you’ve been anywhere near a TV or a radio or a computer in the past few years, you’ll have heard some shocking warnings about climate change that are “based on the science”.


“New study warns of dangerous climate change risks to the Earth’s oceans” (The Guardian July 2015)

“Global warming could be more devastating for the economy than we thought” (The Guardian October 2015)

“For South Asia, Rising Temperatures In India And Pakistan Could Bear Deadly Consequences” (Forbes Magazine, August 2017)

“Global warming to cause 'catastrophic' species loss: study” (CTV News April 2020)

John Robson

These stories, and countless others like them, all share something in common that the authors would rather you didn’t know about. Namely that the “science” in question has a big exaggerated fudge factor that always guarantees a scary forecast.

You see, all of these stories and many studies are based on a global warming scenario called RCP8.5. Which stands for “Representative Concentration Pathway” 8.5. It’s not a forecast. It’s a guess at how much CO2 is going to accumulate in the atmosphere. And it’s not even a realistic guess.

In fact, it was originally presented as an all-but-impossible worst-case scenario. But instead of calling it that, for years scientists and activists have been deceptively referring to it as the “business-as-usual” case, that is, what will inevitably happen if we keep using fossil fuels the way we have in the past.

It’s nothing of the sort. What’s worse, the scientific community has long known that by using it in this way they and others are misleading the public and distorting policy debates. And while some brave souls have begun pushing back against the practice, far too many keep relying on it, not because it’s scientifically valid but because it’s politically useful in scaring people.

For the Climate Discussion Nexus, I’m John Robson, and this is a CDN Fact Check video on the RCP8.5 Scam.


If you want to make a scientific prediction about global warming over the coming century, you’ll need three things.

The first is a guess about how much economic growth will happen over the coming century, and how much carbon dioxide and other greenhouse gases will therefore be emitted from fossil fuel use, and how much will stick around in the atmosphere instead of being absorbed by plants and the ocean.

The second is an estimate of how much any greenhouse gases that do accumulate will change something called “Radiative forcing,” which is the term scientists use to describe the flow of energy in and out of the atmosphere. Energy comes in from the sun, and goes back out as the Earth radiates its heat back to space. If greenhouse gases build up in the atmosphere, according to global warming theory, they trap more of the heat so less can radiate back to space.

The third thing you need, therefore, is a computer climate model to multiply your estimate from step one of GHG accumulation by your estimate of radiative forcing per unit of GHGs, and then predict how temperature, precipitation and all the other features of our climate system will change in response.

John Robson

So, it’s models all the way down. And there’s nothing wrong with using models, as long as researchers don’t build in assumptions they know are biased, including ones that have failed consistently in the past, or claim more certainty for the results of their modeling than logic and evidence warrant.

Now we’ve already talked in our video on Climate Sensitivity about how climate models have been systematically predicting too much warming in response to past emissions compared to historical data. But now we’re going to back up a step and look at the emission forecasts going forward because, if a model overestimates GHG accumulation, it will overestimate temperature increase even if it gets Climate Sensitivity roughly right. And it will doubly overestimate the temperature increase if it overestimates both the accumulation of greenhouse gases and the impact that greenhouse gases have.


About 10 years ago, the Intergovernmental Panel on Climate Change put together four groups of emission scenarios for climate modelers to use when making predictions of 21st century global warming. The scenarios are called “Representative Concentration Pathways” or RCP, and each one has a number attached to it indicating the increase in total radiative forcing.

At the low end, RCP2.6 predicts very little increase in GHGs, and the climate models say it won’t lead to much warming. Next up are RCP4.5 and RCP6.0, which predict more accumulation and hence more radiative forcing and therefore more warming. And at the high end is RCP8.5, which predicts an enormous increase in GHGs. Hence if you plug RCP8.5 into a climate model, it always predicts a climate catastrophe.

John Robson

So, which of these four scenarios is most realistic? Before I show you the answer, there’s good reason to guess it will be the lowest of the lot. Why? Because the IPCC and other climate scientists have a long history of over-predicting CO2 emissions.

Now again, the issue here isn’t how much impact CO2 and other GHGs have. It’s how much GHG accumulation is going to happen or, in the case of many of these predictions, should already have happened but didn’t.

And it turns out that a decade before the RCP scenarios were developed, the IPCC had developed another set called the SRES scenarios. They too spanned a wide range, from hardly any emissions growth to so much that the planet fried to a crisp.


When the IPCC introduced the SRES scenarios for their Fourth Assessment Report, which was released in 2007, there was a lot of attention paid to the fact that the high-end warming prediction had suddenly jumped from 4.5 degrees Celsius, the figure in their 2002 report, to nearly 6 degrees Celsius. But this extra warming didn’t come from the climate models.

They still used the same assumptions about radiative forcing per unit of GHGs. Rather, the surge in temperature came from a new extreme emission scenario called A1FI, which predicted a huge increase in coal use around the world starting in 1990.

John Robson

It was a slippery piece of scare-mongering. It turned out the A1FI scenario hadn’t even been shown to scientific reviewers during the drafting stage. So when the report was published, one of the reviewers wrote to the IPCC Vice-Chairman, Dr. Martin Manning, demanding to know why the top end of the warming range had jumped so much. And Manning replied:

The higher warming projections that arose towards the end of the [review] process are due to a high fossil fuel emissions scenario rather than changes to climate models.

But why was the fuel emissions scenario changed? Well, Manning added, introducing this scenario “was a response to final government review comments for the SRES.”

As usual, it’s the politics, not the science, that’s settled. Government officials demanded that an extreme emission scenario be slipped in at the end, after the close of expert review, and the IPCC said “Sure”. But don’t look so shocked.

If the idea of senior government officials dictating what the IPCC report is supposed to conclude surprises you, take a look at our video on Hiding the Decline. To coin a phrase, it’s business-as-usual.

Now the A1FI scenario projected coal use would soar globally by 31 percent between 1990 and 2000. But that didn’t happen. Instead it fell by 10 percent.

So even by the year 2000, the IPCC knew A1FI had grossly overshot the emission projections. But with politics trumping science, as usual, that knowledge didn’t stop them from making A1F1 the centrepiece of their warming forecasts.


If it were an isolated incident, it might be dismissed as unimportant. But it’s by no means the only time greenhouse gas forecasts have gone off the rails.

Instead, according to a 2019 paper in the peer-reviewed journal Geophysical Research Letters in which a team of American climate scientists compared forecasts of CO2 levels in the atmosphere from the 1970s onwards to observations, the actual growth of CO2 has always been at the low end of whatever range is projected.

John Robson

It’s remarkable to see a branch of science keep making the same mistake over and over. Decade after decade they put out a range of forecasts, then go back and see that they were way too high, then go back and… do the same thing over again.

Well I said it was remarkable. In fact it would be remarkable if we were not dealing with political science here, where it’s verdict first, trial afterward. Which brings us to the RCP scenarios including RCP8.5.

Needless to say, RCP8.5 is off the charts. But even the others are looking suspicious. A recent study by experts from the University of British Columbia and the University of Colorado just showed that GHG emission trends are once again tracking the low end of the RCP range.

This graph shows projected and observed global emissions of CO2. The orange line shows observed emissions up to 2017, and after that it shows expert outlooks from the energy industry, that is, the folks who have to have a realistic idea of how much demand there’s going to be over the next few decades because it’s up to them to keep our lights on and their companies in business. And notice that it’s down near the bottom.

Now look up. Way way up. To the other lines showing the IPCC projections, including the RCP8.5 scenario, which as of 2020 is already hopelessly excessive.

Given the pattern of reinforcing failure in this field of pseudo-science, you won’t be surprised to hear that in response the IPCC has added in a set of new scenarios, called the “Shared Socioeconomic Pathways” or SSPs, some of which go even higher than RCP8.5. As with an addictive drug, you need more and more to get that jolt.


Here it’s important to bear in mind that the world has not taken many significant policy actions to cut greenhouse gas emissions. As we talked about in our videos on the Paris Accord, none of the countries that made pledges under the Kyoto Protocol lived up to their promises, and none of them are living up to Paris either. For 40 years we’ve been experiencing the Business-as-Usual scenario.

What both of these studies show is that the path of emissions under business as usual is right at the bottom end of the range of forecasts. It has been since the 1970s, and it looks like it will continue to be for decades to come.

John Robson

So, if you want to pick a Business-as-Usual scenario, your best bet is to pick the one at the bottom end of the range. Instead those famous climate scientists consistently use RCP8.5, up near the high end, even though they know it was never meant to be treated as a probable or even plausible scenario. If anything, it was a kind of warning boundary: If you got results close to this line, go back and try again, because this one isn’t happening, and they know it.


In a stinging commentary published in Nature magazine last year, two US climate experts put it bluntly about RPC8.5: “the business as usual story is misleading. Stop using the worst-case scenario as the most likely outcome.”

They pointed out that RCP8.5 was supposed to represent an “unlikely high risk future.” Unfortunately, they went on, “it has been widely used by some experts, policymakers and the media as something else entirely: as a likely ‘business as usual’ outcome.”

John Robson

Like the phony A1FI scenario before it, RCP8.5 gets its emission kick from a crazy assumption about coal use. Instead of projecting global coal use per person will keep following its decades-long trend downwards, they’ve invented a future in which coal use suddenly shoots up to unimaginable levels.


Look at this chart of coal use per capita, with the green line showing actual historical data and then various scenarios including RPC8.5 where it more than triples and the new, non-improved SSP5-8.5 where it goes up six-fold. It’s an impossible picture, and it flies in the face of reality. The authors from UBC and Colorado pointed out that the RCP8.5 scenario doesn’t even make sense following its own logic.

John Robson

It assumes so much economic growth that the world’s poorest countries will become wealthier than the richest one are today, which would be great if it happened. But at the same time says they’ll warm so much they’ll be uninhabitable and their economies will collapse. How can both those things happen?


And yet studies based on RCP8.5, and calling it “business as usual”, just keep on coming.

[Reads headline:] Climate change effects that could get worse: Rising heat, storms

[Reads headline:] 2015's record-breaking temperatures will be normal by 2030 - it's time to adapt

[Reads headline:] The World Faces Rising Costs Of Climate Change As Oil Prices Drop

[Reads headline:] 26 Climate Crisis Disasters That Will Get Worse If We Do Nothing

John Robson

These studies and stories all say we’re on the RCP8.5 path unless we change our ways and adopt radical carbon-emission cuts. But the scientists know this is untrue.

The whole point of those radical cuts being pushed on us is to get the world from the dangerous top end of the emission projections down to the safe path along the bottom, where there will be very little warming and manageable consequences. But the truth is, we’re already at the bottom.

For 40 years we’ve been hugging the low end of the emission forecast range, and the data tells us we’re likely to continue doing so for the next 40 years as well. And it’s time for the press and scientists to stop claiming otherwise.


This story, from September 2019, says “RCP2.6 represents the most aggressive approach to reducing global emissions, peaking in 2020 and declining rapidly thereafter. RCP8.5 is more akin to the ‘business as usual’ model.”

John Robson

That’s completely backwards. The lowest emission scenario is the one consistent with a continuation of business as usual. RCP8.5 is an all-but impossible worst-case scenario. The scientists involved all know this, but they keep using misleading scenarios to drum up bigger and bigger scare stories, and possibly research grants.

But now that you know how the game works, when you see a scary climate headline, check the details. And if it’s based on RCP8.5, as it almost certainly is, it goes into the trash where it belongs, and where the scientists know it belongs.

For the Climate Discussion Nexus, I’m John Robson.


5 comments on “The RCP 8.5 Cheat”

  1. Thank you for this excellent video presentation. Even high school students will be able to understand this.
    In Ontario, the citizens were repeatedly told that industrial scale wind turbines foisted on rural communities in our gorgeous Great Lake shoreline communities would 'save the planet'. We now know the deception of the climate science used by our media and politicians. We know that a proper cost/benefit analysis was not done before long term contracts were signed. We also know that health studies were not done to prove that acoustic emissions, both audible and sub audible, from these industrial scale turbines, would not harm the people whose homes were too close or in some cases surrounded by clusters of turbines.
    What we don't know is why why these turbines are still being subsidized and why the long term contracts haven't been cancelled.

  2. Video demonstrates that climate alarmism depends on so many faulty, self-contradictory and deceptive practices that it cannot be termed science at all. This video is only about one stage in the whole dubious chain of climate alarmist "science". Whether or not even hugely increasing CO2 levels would be harmful to humans, let alone catastrophic, is very speculative.

  3. I've shared links to CDN with my son to share with his kids. At least now my grand kids can be stressed about final exams and homework instead of whether or not they will have a planet to live on. Thank you CDN for helping us teach our kids to think .

  4. If you take a look at the material that students are being fed on this subject matter, you'll see all sorts of ways in which, even as they focus on their studies, they're dealing with highly questionable information.
    In the process of regurgitating this information in their assignments, tests and exams, they're being misled.
    If they challenge this information, what happens to their grades?

  5. Thank you for educating people on the climate corruption that is going on today. Working in the O&G industry I always push back on the utter stupidity of government regulators forcing companies to assess their projects using 5 different models. Five! I’ll never stop pushing back against this abuse of science.

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